1. Field of the Invention
The present invention relates to a brushless motor and a manufacturing method thereof.
2. Description of Related Art
Japanese Unexamined patent Publication No. 2008-259407A (corresponding to U.S. Pat. No. 7,659,644B2) teaches a brushless motor, which includes a single vibration damper (vibration isolator) that is made of rubber or resin and is configured into an annular form extending in a circumferential direction of a stator. In this brushless motor, the vibration damper includes inner peripheral recesses, primary recesses (first-side outer peripheral recesses) and secondary recesses (second-side outer peripheral recesses). The inner peripheral recesses of the vibration damper are engaged with outer protrusions, respectively, of the centerpiece. The primary recesses of the vibration damper are engaged with primary protrusions (first-side inner peripheral protrusions), respectively, of the stator, and the secondary recesses of the vibration damper are engaged with secondary protrusions (second-side inner peripheral protrusions), respectively, of the stator.
In the brushless motor of Japanese Unexamined patent Publication No. 2008-259407A, each one of the primary recesses and adjacent one of the secondary recesses of the vibration damper are circumferentially placed between corresponding circumferentially adjacent two of the inner peripheral recesses of the vibration damper. Therefore, in this vibration damper, a volume of a shock absorbing portion, i.e., a damping portion (thick wall portion), which is circumferentially defined between the corresponding inner peripheral recess and the primary recess or the secondary recess, may possibly become insufficient for damping the vibrations in some cases. Therefore, in order to improve the vibration damping performance of the vibration damper, there is required a further improvement.
Furthermore, in the brushless motor that includes the vibration damper, which is held between the stator and the centerpiece and resiliently supports the stator relative to the center piece, it is desirable to achieve a good weight balance of the stator relative to the centerpiece.
Japanese Unexamined Patent Publication No. 2008-301622A (corresponding to U.S. Pat. No. 7,745,964B2) teaches a brushless motor having a plurality of vibration dampers (vibration absorbing members), each of which is made of a metal plate and is placed between a stator and a centerpiece to limit conduction of vibrations, which are generated in the stator, to the centerpiece.
In Japanese Unexamined Patent Publication No. 2008-301622A, the vibration dampers are designed to be installed to the stator individually. Therefore, when a factory assembly worker is trying to install these vibration dampers simultaneously to the stator, the vibration dampers interfere with each other, thereby hindering the assembling of the vibration dampers to the stator. Thus, it difficult to assemble the vibration dampers simultaneously using an automatic assembling machine. Furthermore, it is conceivable that the factory assembly worker manually installs the vibration dampers one by one with his/her hands. However, in such a case costs are disadvantageously increased. Furthermore, in the case where the vibration dampers, which are designed to be individually installed, are used, the number of the components of the brushless motor is disadvantageously increased. Thus, for the manufacturing of the brushless motor, the time required to stock the vibration dampers at the factory is disadvantageously lengthened, thereby resulting in an increase in the costs.
In the case of Japanese Unexamined Patent Publication No. 2008-259407A described earlier, at the time of assembling the annular vibration damper to the stator, engaging portions (recesses) of the vibration damper need to be forcefully engaged to corresponding engaging portions (protrusions), respectively, of the stator. Therefore, it may not be easy to install the vibration damper to the stator.